Field of the Technology
Embodiments of the present invention relate to flow control valves used for controlling the flow rate of fluids.
Description of the Related Art
In a blow-by gas refluxing system of an internal combustion engine of a vehicle, such as an automobile, there has been employed a positive crankcase ventilation (PCV) valve as a flow control valve for controlling the flow rate of blow-by gas.
A conventional example of the PCV valve (hereinafter referred to as “conventional example 1”) will be described. FIG. 19 is a sectional view illustrating a PCV valve. As shown in FIG. 19, a PCV valve 140 is equipped with a tubular housing 142 having an inlet port 143 and an outlet port 144, a valve member 146 arranged inside the housing 142 so as to be capable of moving forward and rearward in the axial direction, and a spring 166 including of a coil spring configured to bias the valve member 146 toward the inlet port 143 (to the right as seen in FIG. 19). A seat 150 having a monitoring hole portion 151 of a predetermined inner diameter is installed inside the housing 142. The valve member 146 is equipped with a base shaft portion 159 and a monitoring shaft portion 160 continuous with the leading end side portion of the base shaft portion 159. The monitoring shaft portion 160 coaxially includes a small-diameter shaft portion 163 on the leading end side, a large-diameter shaft portion 164 on the base end side, and a tapered portion 165 having a diameter increasing from the small-diameter shaft portion 163 side toward the large-diameter shaft portion 164 side. The tapered portion 165 has a predetermined tapering angle θ1. The monitoring shaft portion 160 of the valve member 146 is inserted into the monitoring hole portion 151 of the seat 150. At the base end portion of the valve member 146, there is provided a flange-like guide portion 161. The spring 146 is interposed between the seat 150 of the housing 142 and the guide portion 161 of the valve member 146.
In the above-described PCV valve 140, when the intake negative pressure is introduced into the housing 142 from the outlet port 144 side, the valve member 146 moves toward the outlet port 144 side (to the left as seen in FIG. 19) against the biasing force of the spring 166 in accordance with the difference between the upstream side pressure and the downstream side pressure. As a result, the flow rate of the blow-by gas flowing through an annular opening defined between the circumferential wall of the monitoring hole portion 151 of the housing 142 and the monitoring shaft portion 160 of the valve member 146 is controlled, that is, monitored. PCV valves of a structure similar to that of conventional example 1 are disclosed, for example, in JP-A-2005-330898 and JP-A-2012-163085.
According to conventional example 1 described above, a coil spring of a fixed spring constant is employed as the spring 166. Further, there is a demand for an increase in the flow rate of the blow-by gas in the wide open throttle (WOT) range of the engine. Thus, as the diameter of the small-diameter shaft portion 163 of the monitoring shaft portion 160 of the valve member 146 is reduced, the tapering angle θ1 of the tapered portion 165 increases (that is, the tapering becomes steeper). In the valve member 146 having the tapered portion 165 with a steep tapering angle θ1, the change in flow rate with respect to the distance of movement of the valve member 146 is large in the movement range for monitoring the flow between the monitoring hole portion 151 and the tapered portion 165. In this way, self-excited oscillation is likely to be generated which may lead the flow rate characteristics to become unstable.
A modification (hereinafter referred to as “conventional example 2”) of conventional example 1 described above will be described. FIG. 20 is a sectional view illustrating a PCV valve. The portions of conventional example 2 corresponding to those of conventional example 1 are indicated by the same reference numerals with symbol A added thereto. As shown in FIG. 20, by setting a tapering angle θ2 of a tapered portion 165A of a valve member 146A to a small angle (i.e., a gentle angle), it might be possible to suppress the self-excited oscillation of the valve member 146A, and to stabilize the flow rate characteristics. However, setting the tapered portion 165A to have the gentle tapering angle θ2 may lead to an increase in the axial length of the tapered portion 165A and an increase in the axial length of the large-diameter shaft portion 164A. As a result, the axial length of the valve member 165A as a whole may increase, and, further, the axial length of the housing 142A may increase. Further, this will result in an increase in the movement range or the stroke amount of the valve member 146A, and it is necessary to increase the spring length (axial length) of the spring 166A and to reduce the spring constant thereof. Thus, the size of the PCV valve 140A may inevitably increase.
With the arrangements of conventional examples 1 and 2 described above, it is difficult to achieve both the stabilization of the flow rate characteristics of the PCV valve and the suppression of an increase in the size thereof. This would restrict the degree of freedom in terms of design to a rather low level. Further, the PCV valves as disclosed in JP-A-2005-330898 and JP-A-2012-163085 also involve the same problem as that in conventional example 1. In the case of JP-A-2012-163085, there is provided, in the downstream portion within the housing, a restricting spring for restricting excessive movement of the valve member toward the downstream side. However, the restricting spring is a spring configured to act when the valve member has moved excessively downstream beyond the movement range used for monitoring. In other words, it is not a spring related to the monitoring function.
Therefore, there has been a need in the art for flow control valves that are improved in terms of freedom in design.